Compressor system



Dec. 16, 1947. I H. c. z m 2,432,553

COMPRESSOR SYSTEM Filed April 21. 1943 4 Sheets-Sheet 1 Dec. 16, 1947. H. c. ZILLY COMPRESSOR SYSTEM Filed April 21, 1943 4 Sheets-Sheet 3 lizvenwr: Herert! Zlg .azy

Dec. 16, 1947. H. c. ZILLY COMPRESSOR SYSTEM Filed April 21, 1943 4 Sheets-Sheet 4 lizwnfor:

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Patented Dec. 16, 1947 UNHTED STATES FATENT OFFICE 21 Claims.

This invention relates to control systems for controlling automatically the operation of pumps or compressors.

It is sometimes necessary, where the demand for pressure fluid varies considerably, to provide several compressors with control systems which operate automatically to control the operation of the various compressors in accordance with the demand. The control of the compressors should be such that the capacity of the system may be changed in small increments between a fraction of the output of one compressor and the maximum output of the combined compressors, and such that efficient operation is obtained regardless of the quantity of pressure fluid supplied.

The control systems of this invention are adapted to such control. If a large quantity of pressure fluid. is needed and there is but little change in the need, all of the compressors are connected to operate, but the control system for one of the compressors operates automatically to unload and reload itscompressor in steps as the demand varies. If the need for pressure fluid decreases and the discharge pressure increases even when the compressor on step control is completely unloaded, then the other compressors are unloaded completely one at a time. The control systems are adapted to effect a reloading of the latter compressors if the discharge pressure drops certain amounts Within predetermined time period's, but otherwise cause their driving motors to be stopped. After the driving motors have been stopped, they are not started again until minimum discharge pressures have been reached.

The compressor operating on step loading and unloading is driven continuously, and is reloaded in steps at pressures somewhat above the minimum pressures at which the driving motors for the other compressors are started. This compressor then operates alone or in combination with any of the other compressors whose driving motors were not stopped, to carry the load. In order that each of the compressors may be subjected to the same amount of wear, means are provided for making the control systems selectively operative to effect step control by any one of the compressors while the others operate on complete loading and unloading with a starting and stopping of their driving motors.

An object of this invention is to provide an improved control. system for pumps or compressors.v Another object is to provide an improved control system for a plurality of pumps or compressors delivering fluid to a common discharge line, said control system operating automatically to control the operation of the pumps or compressors in accordance with the pressures in the discharge line. Still another object is to provide for a plurality of compressors deliverin fluid into a common discharge line and an improved control system for each compressor, with each control system being selectively adjustable to provide different controlled operations of its respective compressor. Yet another object is to provide an improved compressor system including a plurality of compressors and automatic control means therefor, said, control means providing stepped loading and. unloading for at least one of the compressors and complete loading and unloading at different discharge pressures for the other compressors. Still another object is to provide improvedcontrol means for a plurality of compressors discharging into a common discharge line, said control means being selectively operative to eifect stepped loading and unloading during continuous operation of any one of the compressors, and complete loading and unloading at different pressures of the other compressors with a starting and stopping of their driving motors. Yet another object of this invention is to provide improved control systems for a plurality of compressors, said control systems being selectively operative to provide stepped loading and unloading or complete loading and. unloading of the compressors, with unloading taking place when control circuits of the systems are de-energized so that a gradual stopping of the com-: pressors may be assured at all times, These and other objects of my invention will hereinafter more fully appear.

In the accompanying drawings in which two illustrative forms of the invention have been shown:

Fig. 1 is a schematic View of a compressor system having the improved control means incorporated therein.

Fig. 2 includes a schematic diagram of one of the compressors and an enlarged view of the control system therefor, parts being shown in section.

Fig; 3 is an enlarged sectional view through a portion of a lower pressure cylinder and its intake connection.

Fig. 4 is an enlarged sectional view through a portion of a high pressure cylinder and unloading means therefor.

Fig. 5 is a view similar to that of Fig. 2 but showing a modification of the invention.

In the illustrative embodiment of the invention shown in Figs. 1 to 4, compressors I, 2, 3 and 4 discharge into a common discharge line 5 and have individual control systems, generally designated 6, i, 8 and 5-]. It will be understood that the number of compressors and control systems is not at all necessarily limited to four, but this number has been shown because it indicates conveniently the variations of control that may be obtained.

Each of the compressors is multi-stage and includes a pair of double acting low pressure cylinders H, H and a pair of double acting high pressure cylinders l2, l2. Fluid is supplied to the low pressure cylinders through intake connections [4, I5, and is compressed in the low pressure cylinders and is then delivered through intercoolers I5, 55 to the high pressure cylinders where it is compressed again and then delivered through connections l6, 15' to a common conduit l'l communicating with the discharge line 5. These compressors are merely illustrative of a type of compressor that is suitable for use with the control systems or this invention. Any compressor that is capable of step controlled loading and unloading may be used.

As shown in Fig. 3, an intake closure valve i9 is provided in each of the intake connections to the low pressure cylinders. Each valve I9 is provided with a stem 20 carrying a piston 2B which is reciprocably mounted in a bore 22. Surrounding the valve stem is a coiled spring 23 acting against the piston 2! for holding the valve normally in its open position. Pressure fluid may be supplied through a port 2 5 to the outer end of the bore 22 where it acts on the piston 2| and forces the latter, against the spring 23, to close the valve i9. At the ends of each low pressure cylinder are inlet valves 25 for controlling the flow of fluid between the intake connection and the bore 26 of the cylinder, and discharge valves, not shown, for controlling the flow of fluid between the cylinder bore 26 and the intercooler. The inlet valve at the head end of each low pressure cylinder is adapted to be held open by a suitable fluid actuated device 21 for unloading that end of the cylinder.

The unloading device 2'! herein comprises a diaphragm 29 clamped within a chamber 3!! and carrying fingers 3! which are adapted to engage the inlet valve and move the latter from its seat. The fingers 3| are normally held out of engagement with the valve by a spring 32 acting on the lower surface of the diaphragm, and may be moved in a valve opening direction by pressure fluid supplied through passage means 34 to the outer side of the diaphragm.

The high pressure cylinders 12, i2 are provided with suitable inlet and discharge valves, not shown, and one of the inlet valves in the head end of each of the high pressure cylinders is adapted to be held open, as shown in Fig, 2, by an unloading device 36 similar to the unloading device 21. The high pressure cylinders are also provided, as shown in Fig. 4, with pressure responsive means, generally designated 38, for effecting an unloading, herein shown as by venting to the atmosphere, of the ends of the high pressure cylinders when their respective intercoolers have been pumped down until a subatmospheric pressure exists therein.

The unloading means 33 comprises a diaphragm 4t clamped within a chamber M and subjected on its upper side to intercooler pressure through a connection 42 and on its lower side to atmospheric pressure through an opening 43. A stem 44 is clamped to the diaphragm Ml and is adapted to engage a valve 45 and move the latter from its seat against the action of a spring 46 for connecting a passage 4'! to atmosphere through a chamber 48. The passage 51 communicates at opposite ends of the high pressure cylinder with chambers 4-9 containing check valve mechanisms 5%, herein a pair of the regular discharge valves of the high pressure cylinder.

The compressors may be individually unloaded in steps as follows: Pressure fluid is supplied first, as shown in Fig. 2, to the unloading devices 2? and 36 in the head ends of the low pressure cylinder I l and the high pressure cylinder 12. At a predetermined increase in discharge pressure the head ends of the low pressure cylinder I I and the high pressure cylinder I2 are unloaded by opening the inlet valves in these ends. The third step of unloading is efiected by supplying pressure fluid to close the intake closure valve IS in the intake connection for the low pressure cylinder H. The fourth step of unloading takes place when the intake closure valve in the intake connection I l to the low pressure cylinder l l is closed. The loaded ends of the high pressure cylinders continue to pump fluid from their intercoolers to the supply line 5 even after the supply of fluid to the intercoolers has been completely cut ofi by the closing of the intake closure valves. When the pressure in the intercooler is reduced to subatmospheric, the diaphragm 4?} of the unloading device 38 is forced inwardly by the atmospheric pressure acting on its outer side and causes the valve @5 to be unseated by the stem 44. The passage l then communicates past the valve 15 to atmosphere through the chamber 48, and any pressure fluid in the chambers 49 escapes through the passage 31 so that the valves 50 are opened when the pressures at the ends of the high pressure cylinder bore exceed atmospheric by a small amount, and the small amounts of fluid that may be compressed in the high pressure cylinders during unloaded operation are discharged to atmosphere.

Reciprocably mounted within the low and high pressure cylinders are pistons 52 and 53 having piston rods 54 and 55 connected to a common crankshaft, not shown, for actuation thereby. A separate power unit 56, shown herein as an electric motor, is provided for driving each crankshaft.

The control systems 6, l, 8 and 9 are herein identical, and each comprises, as shown in Figs. 1 and 2, solenoid controlled valves 6!], 6!, 62 and 63 having control circuits which may be opened and closed separately respectively by pressure responsive switches Ed, 65, 65 and 6'! when the compressor operates on step loading and unloading, and which may be opened and closed simultaneously by a pressure responsive switch 68 when the compressor operates on completeloading and unloading. A manually operated switch it! is provided to enable selective step control or complete loading and unloading control.

Each of the solenoid controlled valves 60, El, 62 and 63 includes a casing it having chambers 12 and i3 communicating, respectively, through ports '54 and T5 with a chamber 16. The chambers F2 are connected by branch conduits 1?, 18, it and 8*] to a common conduit 3! opening into the compressor discharge line 5, and the chambers F3 are connected to atmosphere through exhaust ports 82. The chamber 15 of the valve 60 is connected by a conduit 83 and branch conduits 8t and 85 to the unloading devices 27 and 36 of the low and high pressure cylinders H and I2.

The chamber 16 of the valve BI is connected through a conduit 86 and branch conduits 81 and 88 to the unloading devices 2'! and 36 of the low and high pressure cylinders II and I2. The chambers '55 of the valves 62 and 63 are connected, respectively, by conduits 89 and 90 to the ports 24 in the intake closure valve operating cylinders associated with the intake connections I4 and It. Extending through the ports I4 and i5 is a valve stem 92 carrying valve members 93 and M which are adapted to engage valve seats surrounding the ports 74 and i5 and cut off communication between the chamber I5 and the chambers '52 and it. The valve stem is held normally by a spring 95 in a position to seat the valve member 95 and unseat the valve member 94. Attached to one end of the valve stem is a plunger 55 which is pulled by the magnetic force of an associated solenoid, later described, when the latter is energized, in a direction to seat the valve member 94 and unseat the valve member at.

Solenoid windings 5?, 95, 99 and IGII are provided for the valves 56, 5!, 52 and 53 respectively; and these windings are connected at one end to a common conductor IIlI leading to a terminal 552 of a switch I 53 which forms part of a motor starting device later described. The other terminal ltd of the switch is connected by a conductor hi5 to one side L1 of a power line. The opposite ends of the solenoid windings 9?, 98, 99 and I55 are connected, respectively, to conductors I 55, ml, I68 and E59 leading to contacts H0, III, H2 and MS of the pressure responsive switches 64, 55 6?. These same ends of the solenoid windings are also connected by conductors II4, I55, its and ill to contacts of a solenoid operated switch IIS which is normally held in an open position. by a spring H9. The other contacts of the switch I68 are connected by a conductor 28 to a contact 52! of the pressure responsive switch 58. Another contact I22 of the switch 68 is connected by a conductor I 23 to a third contact 524 of the switch 68, and the contact 52 is connected by a conductor I25 to a contact I25 of the manually operated switch Ill. The pressure responsive switches 64, 55, 65 and 63 are provided with contacts I21, I28, I29 and I3!) connected by a common conductor I3I to a contact 532 of a solenoid operated switch I33 which I is normally held in a closed position by a spring NM. The switch I33 is provided with another contact I35 which is connected by a conductor I36 to the other side L2 of the power line.

Each driving motor 55 for the compressors is provided with an automatic starting device I40, as shown in Fig. 1. This starting device is of stand ard construction and includes the switch I53, motor switch devices and a suitable solenoid operating means, not shown, the solenoid operating means acting when energized to close the motor switch devices and the switch I63, the latter being preferably closed when the starter reaches running position. One terminal of this solenoid is connected by a conductor MI to the power line L1 and the other terminal is connected through one of two circuits to the power line L2. One of the circuits includes a conductor I42 extending from the device to a contact Hi3 of the manually operated switch is, the contactor of the switch Til, and a wire I54 connecting the contactor to the power line L2. The other circuit includes the conductor I42, a conductor I45 branching from the conductor I42 and connected to a contact I45 of a solenoid operated switch I41, and

a conductor I48 extending from the other contact I49 of the switch I41 to the power line L2. The switch I4? is normally held in an open position by a spring I50.

The solenoid operated switches I33, H3 and it! are provided with solenoids I52, I53 and I54, respectively connected at one end by conductors 555, I55 and I5? to the power line L1. The other ends of the solenoids are connected by conductors E58, I5t and I to a common conductor iBI leading to a contact I52 of a time relay I63. The other contact I64 of the time relay is connected by a conductor I65 to the contact I 26 of the manually operated switch 10. The time relay IE3 is normally held in an open position by a spring I51, and is provided with a solenoid I58 which effects, when energized, immediate closure of the relay and delays, on ole-energizing, the opening of the relay for a predetermined period of time. One end of the solenoid I68 is connected by a conductor its to the power line L2, and its other end is connected by a conductor M8 to a contact ITI of the pressure responsive switch 68.

The pressure responsive switches 64, 65, 65, 51 and 58 may be of any suitable type, and are shown .herein as being actuated by diaphragms I13 to which pressure fluid is supplied from the pressure discharge line 5 through the conduit 8I and a branch conduit I'M. The switches 64, 65, 65 and 5? of the control system for each compressor are adjusted to operate successively at pressures Within a range of to pounds. In this case the switches 54, 65, E6 and 61 close successively at pressures of 94, 96, 98 and 100 pounds and open again as the pressure drops a pound or two below that at which each switch closed. The pres sure responsive switches 68 of the control circuits 5, I, 8 and 9 normally assume positions to connect the contacts I24 and Ill and operate successively at pressures exceeding 100 pounds, herein at pressures of 101, 102, 103 and 104 pounds, to connect the contact I2I, I22 and to break the connection between the contacts I24, I'II. After the switches 68 have once moved to their upper positions connecting the contacts I 2I,' I22, they remain in such positions until the pressure drops to values somewhat below those at which the pressure switches 64, 65, 66 and 6'! operate. The switches 68 of the circuits 6, I, 8 and 9 herein drop successively to their lower positions conmeeting the contacts I2 3, I'll at line pressures of 86. 87, 88 and 89 pounds.

The operation of the compressor system is as follows. Assume that compressor I is to operate on step controlled loading and unloading with continuous operation of its motor, and that compressors 2, 3 and 4 are to operate on complete loading and unloading with a stopping and starting of their driving motors in accordance with the demand for fluid, The manually controlled switch ID of control circuit 6 will be moved to a position connecting contact I43 to the conductor I44 leading to the power line L2, and the switches II! of the control circuits I, 8 and 9 will be moved to positions connecting contacts I26 to the conductor I44.

The control circuit 6 then provides for the motor starting device I 40 of compressor I a circuit including the conductor I4I connecting one side of the device I40 to the power line L1, and the conductor I42, switch 10 and conductor I44 connecting the other side of the device to the power line L2. Current flows continuously through this circuit and keeps the driving motor for compressor I running and the switch I53 assesses closed. The pressure responsive switches 64, 65, .66 and 61.havetheir contacts I21, I28, I29 and lidlleconnected to the power line L2 through the conductor I3I, switch I33 and conductor I36, and, .since thesolenoid i152 for switch 133 will be deenergized at this time, the switch will be held closed by the spring 134 to maintain thisportionofthe circuitcomplete. The other-contacts .110, III, H2 and IIS ofthe switches are connected .continuouslythrough the solenoids .91, 98, .991and I00, conductor IDI, switch I83 and confductor I05 to the power line L1.

When .the pressurein the compressor-discharge line 5 increases to 94.pounds, the pressure switch 64 .closes and energizes the .solenoid 91, causing the valve member 23 to move from its seat and thevalve members-i to engage its seat. Pressure fluid then flows from .conduit 81 through chamber .12, port; 1.4, chamber 16, conduit 83 and branch conduits .84 and 85 to the unloading devices 2! and .36 for unloading the head ends of the low and high pressure cylinders II and 52. If the pressure continues to increase, the pressure switches 65, 56 and 6'? close successively at 96, 98 and .100 pounds pressure and energize the solenoids98, 99 and Iilil for operating the valves SI, 62 and 63. When the valve BI is operated by its solenoid, .pressure fluid is supplied from the con- 'duit BI and the branch conduit 18 through the valve to the conduit 36 which conducts it to the branch conduits 8'! and 88 leading to the unloadingdevices 127. and 36 in the head ends of the low and high pressure cylinders II and I2. As the valves 52 and 63 are operated by their solenoids, pressure "fluid is supplied through the conduits 89 and 98 to close the intake closure valves in the intake connections for the low pressure cylinders. If the pressures in the supply line drop to values at which "the pressure switchesfi l, 6,5, 66 ands6'i open, the valves 66, SI, 62 and'BB operate to vent fluid from the unloading connections through the vent ports 82.

Each of the control circuits 1,8 and'9 provides a circuit for the motor starting device I45 of its respective compressor. This circuit includes the conductor I4! connecting the power line L1 to one side of the device M9, and the conductor I42, the conductor M5, the switch Nil and the conductor I48 connecting the other side of the device 140130 the power line L2. 'The switch 'I il'will be open, however, until its solenoid IE4 is energized.

If, with the switches lilen-ga'gingthe contacts I26,the pressure in the compressor 'dischargeiline is such that the pressureresponsive switches "68 associated with compressors 2, 3 and'4 engage the contacts I24 and lit-current will now in .each control system from the power line L1 through the solenoid I63 of the time relay 163;.through the conductor I10, the pressure switch 68, the conductor I25, the switch 15!,8I'ldith8 conductor I44 to the power line L2, Thus .the'timezrelay l53 will be closed and complete circuits through thesolenoids I52, 153 and i5 5 forthe switches I33, H8 and IN. As current .fiOWS'thIOUghTthG solenoid I52, the switch I33will occupy its open position and break the circuit to the pressure responsive switches G4, 65, E6 and 51. Whenthe solenoidlE-S is energized, the switch IiJS is closed and completes circuits'from the valvesolenoids crease and Ieil-to the contact I2i of thepressure responsive switch 58, thus establishing a condition in which an increase to apredetermined value of compressor discharge pressure can eliect complete unloading. With the .energizing of the-solenoid ltttherswitch .tfillisiclosed and completes the circuit through the motor startingdevice I40 so that the motor 56 is caused to run and the switch I533 is closed.

.If the demand for air is less than the amount supplied by the compressor system, the pressure in the supply'line will increase and, at a pressure :of .102 pounds, cause the pressure switch 68 'ofthe control system i to operate and break the connection between contacts I24, Hi and to connect the contacts I2I, I22. When the connectionbetween contacts I25, IEI is broken, the supply ofcurrent through the solenoid I68 for the time relay I63 iscut olf. The relay I63 remains closed, however, for a predetermined length of time and maintains the circuits through the solenoids-for the switches [33, H8 and I41. Since the switch I-I8 will be held in a closed position by its solenoid I53, circuits will be established through the valve solenoids 91, 98, s9 and I00 as soonasthe pressure switch 58 connects the contacts I2! and I22, and the compressor will be completely unloaded. The compressor driving motor will continue to operate since the switch i l-i will be held closed by its solenoid I54. If the pressure in the supply line drops to 8'? pounds, the pressure at which the switch 68 of control circuit l moves to a position connecting the contacts I24 and lli, before the 'end of the time period at which the time relay IE3 opens, the compressor willbe reloaded by the breaking of the circuits through the solenoid relays at the contacts IZI and I22 of the switch 68, and the solenoid I68 for the time relay will be i e-energized to maintain the motor circuit closed. If, however, the pressure in the supply line remains above Bl pounds to the end of the time period, the time relay 2'53 opens and cuts off the flow or" current through the solenoids for the switches I33, H8 and Ml. The switch I33 closes and the switch i i8 opens placing the circuits through the valve solenoids under the control of the pressure switches 84, 85, 56 and 6? so that the system may be changed, if desired, to step control by moving theswitch ie to contact I43. However, it hould be noted that the switch i i? opens and cuts off the supply of current to the driving motor so that it stops and remains stopped until the sole noid for the time relay is again energized.

Whenever the pressure in the supply line increases to 103 pounds, the control system 8 cperates in the same manner as the control system 'l-to unload its compress-or, and, if the pressure doesntdrop to 88 pounds before the end of the time period for which its time relay I63 is adjusted, to stop its driving motor. At 104 pounds pressure in the supply line, the control system Q-operates in the same manner as control sysems "i ends to unloadits compressor and to stop the motor if the pressure doesnt drop to 89 pounds within a predetermined time period.

'There is shown in Fig.5 a modification of the invention in-which the solenoid controlled valves 6376i, 62' and -63 are held in positions for effecting an unloading of the compressor when their windings are do-energized, and are moved to positions for venting the unloading means when "their windings are energized. It will be understood that, as in the first form of the inventiorneach of a plurality of compressors in a system is provided with a control similar to that of Fig. 5. It will be seen that with this arrangement the compressor will be unloaded if the pow-er' should be inadvertently 'cut off and the compressor -w'ill gradually'cometo a stop. To effect this controhpressure 'fluid is supplied from the discharge line through the conduit BI and the conduits 'I'I, it, It and 8]] to the chambers 13 in the casings ll of the valves, and the chambers "I2 in these valve casings are vented to atmosphere. Pressure responsive switches 64, 65, 66, 6? and 68' are arranged to open circuits leading to the solenoid windings of the valves 653, GI, 62 and 63 when the discharge pressure reaches predetermined maximum values instead of closing these circuits as in the first form of the invention. The switch 68' also acts to close the circuit through the winding for the solenoid I68 when the discharge pressure reaches a predetermined maximum value instead of opening it. A time relay IE3 is normally held in closed position by the spring I61 and is opened after the solenoid I68 has been energized a predetermined period of time, this being directly opposite to the control of the relay I63 in the first form of the invention. Other than the changes mentioned above, this second form of the invention is the same as the first. In this case, however, the motor starting device I40 has been shown more in detail, though still in diagrammatic form, there being a solenoid IIBIJ connected to the conductor I42 and to the conductor I85 leading to the power line L1 for controlling the switch I03 and switches I8I and I32 connecting the motor 56 across the power lines L1 and L2.

When the manually controlled switch It: is moved to a position engaging contact I43, a circuit is completed from the power line L1 through conductor I85, the solenoid I83, conductor I42, switch it) and conductor I i l to the power line L2. Current flowing through the solenoid I80 causes the switches I03, I 8| and I82 to close connecting the motor across the power lines L1 and L2, and connecting one end of each solenoid winding for th valves 66, El, I32 and 63" to the power line L1. If the compressor discharge pressure is low, the pressure switches 64, 85', 66 and 61" are closed, connecting the opposite ends of the solenoid windings through the conductor I3I, the switch I33 and the conductor I36 to the power line L2. Under these conditions the valves 60', BI, 62' and I33 are held by their energized solenoids in positions to vent the compressor unloading devices and cause the compressor to operate loaded. As the discharge pressure in creases, the pressure switches 64', 65, 66' and El operate successively to open the circuits deenergizing the valve solenoids and permitting the valves to move to positions for supplying pressure fluid to the unloading devices thereby effecting a step by step unloading of the compressor.

When the switch ill is moved to the contact I26 and the discharge pressure is low, circuits will be established immediately from the power line L1 through the windings of the solenoids I52, I53 and I56, through conductor IEiI, time relay I53, conductor I85, switch it, and conductor Hi l to the power line L2. The energized solenoid I52 causes switch I33 to open and break the circuits controlled by the pressure switches E 5, t5, t5 and ti. Solenoid 553 causes switch II 8 to be closed connecting the solenoid windings for the valves 56', 5i, E2 and 63 through the conductors II S, H5, H6 and II? to the conductor I29 which leads to the contact 52! of the switch 58. With low discharge pressure, the switch Gil assumes a position connecting contacts IZI and I22 so that conductor I20 is connected through conductors I23 and I25, switch I0, and conductor I4 1 to the power line L2- The solenoid windings for the valves are then energized and hold the latter in positions for venting the unloading devices. If the discharge pressure increases to a point where the switch 68 breaks the contacts I2I, I22 and connects the contacts I24, I'll, the circuits through the solenoid windings for the valves are broken causing the latter to move to positions for supplying pressure fluid to the unloading devices, and a circuit is completed through the solenoid I68 for the time relay I63. If the solenoid I58 is energized for a; predetermined period of time, the relay I63 opens, breaking the circuits through the windings of the solenoids I52, I53 and I54. This causes the compressor motor to stop with the compressor cylinders held unloaded until the pressure drops to a value at which the pressure switch operates to break the contacts I24, I'II. If the pressure drops so that the switch 68 breaks the contact between I24, I11 before the time period of the relay I53 elapses, the relay I63 remains closed and causes the motor to drive the compressor unloaded until the contacts IZI, I22 are again connected, at which time the compressor reloads.

Any one or more of the control systems of either form of the invention may be adjusted to effect step controlled operation of their respective compressors by simply moving the respective switch 15 to contact I 43, and the other systems may be adjusted to effect complete loading and unloading of their compressors with motor stopping and starting by moving their switches Ill to contacts I26. It will be noted that the maximum pressure in the compressor discharge line may vary one pound as the difierent control systems are connected one at a time to provide step control while the others provide complete control. When the control system 9 is adjusted to step control, the maximum pressure will be 103 pounds, the pressure at which the switch 68 for the control system 8 operates. When any one of the other control systems is adjusted to step control, the maximum pressure will be 104 pounds, the pressure at which switch 68 for control system 9 operates. The minimum pressures in the supply line may vary in the same manner between 86 and 87 pounds.

As a result of this invention there is provided an improved control of the operation of a plurality of compressors. By providing step control for one of the compressors, a very small quantity of air may be provided when needed, or slight changes in the demand for air may be easily taken care of even when the quantity of air needed is large. The complete loading and unloading of certain of the compressors takes care of the large changes in the demand for air, and the stopping and starting of the driving motors for these com pressors assures efiicient operation. Other advantages 0f the invention will be clearly apparent to those skilled in the art.

While I have, in this application, specifically described two forms which the invention may assume in practice, it will be understood that these forms of the same are shown for purposes of illustration and that the invention may be modified and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent is:

1. In a compressor system, in combination, a plurality of compressors and power units for driving the same, a common discharge line for said compressors, unloading means for each of said compressors, and automatic control systems for controlling said unloading means, said control systems being responsive to compressor discharge pressures and selectivel operative to effect automatically step unloading and reloading or complete unloading and reloading of any one of said compressors.

2. In a compressor system, in combination, a plurality of compressors and power units for driving the same, a common discharge line for said compressors, unloading means for each of said compressors, and automatic control systems for controlling said unloading means and said power units, said control systems being responsive to compressor discharge pressures and selectively operative to effect automatically step unloading and reloading with continuous driving or complete unloading and reloading with stopping and starting of any one of said compressors.

3. In a compressor system, in combination, a plurality of compressors delivering fluid to a common discharge line, motors for driving said compressors, fluid actuated unloading means for each of said compressors, and an automatic control system for each compressor responding to the pressures in said discharge line for controlling the flow of pressure fluid relative to its unloading means, said control system being selectively operative to control automatically the flow of fluid relative to said unloading means so as to eflect step unloading or complete unloading of the compressor controlled thereby.

4. In a compressor system, in combination, a plurality of compressors delivering fluid to a common discharge line, motors for driving said compressors, fluid actuated unloading means for each of said compressors, and an automatic control system for each compressor responding to the pressures in said discharge line for controlling the flow of pressure fluid relative to its unloading means and the supply of operating medium to its driving motor, said control system being selectively operative to efiect automatically step unloading With continuous operation, or complete unloading with stopping and starting, of the compressor controlled thereby.

5. In a compressor system, in combination, a plurality of compressors delivering fluid to a common discharge line, motors for driving said compressors, fluid actuated unloading means for each of said compressors, and an automatic control system for each compressor responding to the pressures in said discharge line for controlling the floW of pressure fluid relative to its unloading means and the supply of operating medium to its driving motor, said control system being selectively operative to elTe-ct automatically step unloading at predetermined discharge pressures With continuous operation, or complete unloading at a higher predetermined discharge pressure with a stopping of the compressor controlled thereby.

6. In a compressor system, in combination, a plurality of compressors delivering fluid to a common discharge line, motors for driving said com-- pressors, fluid actuated unloading means for each of said compressors, and an automatic control system for each compressor responding to the pressures in said discharge line for controlling the flow of pressure fluid relative to its unloading means, said control system being selectively operatlve to effect step unloading at predetermined pressures in said discharge line or complete unloading at a higher predetermined pressure said discharge line.

*7. In a compressor system, in combination, a plurality of compressors delivering fluid to a common discharge line, motors for driving said compressors, a plurality of fluid actuated unloading devices for each of said compressors, and a control system for each compressor responsive to the pressures in said discharge line for controlling the flow of fluid'relative to said unloading devices, said control system including valve means controlling the flow of fluid to each of the unloading devices or" the compressor controlled thereby, and means including devices responsive to the pressures in the discharge line for control ling the operation of said valve means, said last mentioned means being selectively adjustable to effect either a successive or a simultaneous operation of said valve means.

8. In a. compressor system, in combination, a plurality of compressors delivering fluid to a common discharge line, motors for driving said compressors, a plurality of fluid actuated unloading devices for each of said compressors, and a control system for each compressor responsive to the pressures in said dicharge line for control ling the flow of fluid relative to said unloading devices, said control system including valve means controlling the flow of fluid to each of the unloading devices of the compressor controlled thereby, and means including devices responsive to the pressures in the discharge line for controlling the operation of said valve means, said last mentioned means being selectively adjustable to effect either a successive operation of said valve means at predetermined discharge pressures or a simultaneous operation of said valve means at a higher predetermined discharge pressure.

9. In a compressor system, in combination, a plurality of compressors delivering fluid to a common discharge line, motors for driving said compressors, a plurality of fluid actuated unloading devices for each of said compressors, and a com trol system for each compressor responsive to the pressures in said discharge line for controlling the flow of fluid relative to said unloading devices, said control system including solenoid actuated valve means controlling the flow of fluid to each of the unloading devices of the compressor controlled thereby, and means including switch mechanisms responsive to the pressures in the discharge line for controlling the energizing of said solenoids.

10. In a compressor system, in combination, a plurality of compressors delivering fluid to a common discharge line, motors for driving said compressors, a plurality of fluid actuated unloading devices for each of said compressors, and a control system for each compressor responsive to the pressures in said discharge line for controlling the flow of fluid relative to said unloading devices, said control system including solenoid actuated valve means controlling the flow of fluid to each of the unloading devices of the compressor controlled thereby, and means including switch mechanisms responsive to the pressures in the discharge line for controlling the energizing of said solenoids, said last mentioned means being selectively adjustable to efiect either a successive or a simultaneous energizing of said solenoids.

11. In a compressor system, in combination, a plurality of compressors delivering fluid to a common discharge line, motors for driving said compressors, a plurality of fluid actuated unloading devices for each of said compressors, and a control system for each compressor responsive to the pressures in said discharge line for controlling the flow of fluid relative to said unloading devices, said control system including solenoid actuated valve means controlling the flow of fluid to each of the unloading devices of the compressor controlled thereby, and means including switch mechanisms responsive to the pressure in the discharge line for controlling the energizing of said solenoids, said last mentioned means being selectively adjustable to effect either a successive operation of said valve means at predetermined discharge pressures or simultaneous operation of said valve means at a higher predetermined pressure.

12. In a compressor, in combination, a plurality of compressors delivering fluid to a common discharge line, motors for driving said compressors, a plurality of fluid actuated unloading devices for each of said compressors, a control system for each compressor for controlling the flow of fluid relative to said unloading devices, said control system including means operating at different predetermined pressures in the discharge line for connecting said unloading devices successively to fluid supply and exhaust, means operating at a higher and a lower discharge pressure for connecting said unloading devices simultaneously to fluid supply and exhaust, the higher and lower discharge pressure for each control system being different, and means for selectively rendering one of said last two mentioned means eflective and the other ineffective.

13. In combination, a compressor, a motor for driving said compressor, a plurality of fluid actuated unloading devices for said compressor, a control system for controlling the flow of fluid relative to said unloading devices, said control system including valve means controlling the flow of fluid to said unloading devices, and means for controlling the operation of said valve means in accordance with compressor discharge pressures, said last mentioned means being selectively adjustable to effect either a successive or a simultaneous operation of said valve means.

14. In combination, a compressor, a motor for 7 driving said compressor, a plurality of fluid actuated unloading devices for said compressor, a control system for controlling the flow of fluid relative to said unloading devices, said control system including valve means controlling the flow of fluid to said unloading devices, and means for controlling the operation of said valve means in accordance with compressor discharge pressures, said last mentioned means being selectively adjustable to eflect either a successive operation of said valve means at different predetermined discharge pressures or a simultaneous operation of said valve means at a higher predetermined discharge pressure.

15. In combination, a compressor, a motor for driving said compressor, a plurality of fluid actuated unloading devices for said compressor, a control system for controlling the flow of fluid relative to said unloading devices, said control sys tem including means operating at different predetermined compressor discharge pressures for supplying pressure fluid successively to said unloading devices, means operating at a higher predetermined discharge pressure for supplying pressure fluid simultaneously to said unloading devices, and means for selectively rendering one of said last two mentioned means efiective and the other ineffective.

16. In combination, a compressor, a motor for driving said compressor, a plurality of fluid actuated unloading devices for said compressor, a control system for controlling the flow of fluid relative to said unloading devices, said control system including means operating at diiferent predetermined compressor discharge pressures for connecting said unloading devices successively to fluid supply and exhaust, means operating at higher and lower discharge pressures for connecting said unloading devices simultaneously to fluid supply and exhaust, and means for selectively rendering one of said last two mentioned means efiective and the other ineffective.

17. In a compressor system, in combination, a plurality of compressors delivering fluid to a common discharge line, power means for driving said compressors, a plurality of fluid actuated unloading devices for each of said compressors, and a control system for each compressor responsive to the pressures in said discharge line for controlling the flow of fluid relative to said unloading devices, said control system including solenoid actuated valve means controlling the flow of fluid to each of said unloading devices and operative when energized to vent pressure fluid therefrom, and means including normally closed switch mechanisms responsive to the pressures in the discharge line for controlling the energizing of said solenoids, said last mentioned means being selectively adjustable to effect either a successive or a simultaneous energizing and deenergizing of said solenoids.

18. In a compressor system, in combination, a plurality of compressors delivering fluid to a common discharge line, power means for driving said compressors, a plurality of fluid actuated unloading devices for each of said compressors, and a control system for each compressor responsive to the pressures in said discharge line for controllin the flow of fluid relative to said unloading devices, said control system including solenoid actuated valve means controlling the flow of fluid to each of said unloading devices and operative when energized to supply pressure fluid thereto, and means including normally open switch mechanisms responsive to the pressures in the discharge line for controlling the energizing of said solenoids, said last mentioned means being selectively adjustable to effect either a successive or a simultaneous energizing and de-energizing of said solenoids.

19. In a compressor system, in combination, a plurality of compressors delivering fluid to a common discharge line, power means for driving each of said compressors, unloading means for each of said compressors, and an automatic control system for each compressor responding to the pressures in said discharge line for controlling the operation of the unloading means for the compressor controlled thereby, said control system being selectively operative to effect step unloading and reloading or complete unloading and reloading of said compressor.

20. In a compressor system, in combination, a plurality of compressors delivering fluid to a common discharge line, power mean for driving each of said compressors, unloading means for each of said compressors, and an automatic control system for each compressor responding to the pressures in said discharge line for controlling the operation of the unloading means for the compressor controlled thereby and for controlling its driving, said control system being selectively operative to eflect step unloading at predetermined discharge pressures with continuous driving, or complete unloading at a higher predetermined discharge pressure with a stopping of said compressor after a predetermined time delay.

21. In combination, a compressor, power means for driving said compressor, a plurality of unloading devices for said compressor operative to effect either a stepped loading and unloading or a complete loading and unloading of said compressor, a control system for controlling the operation of said unloading devices, said control system including a plurality of means each 0; erative to effect an operation of one of said unloading devices, and means'for controlling the operation of said plurality of means in accordance with compressor discharge pressure, said last mentioned means being selectively adjustable to effect either a successive or a simultaneous operation of said plurality of means.

HERBERT C. ZILLY.

REFERENCES crrnn The following references are of record in the file of this patent: 

